Synthesis and Luminescence Properties of Cycloplatinated Complexes with a Chelating N∧C Pyridine-Derived N-Heterocyclic Carbene - Influence of 2,4,6-Triphenyl­phosphinine versus Triphenylphosphine

Two cycloplatinated complexes of the form [Pt(NC)CH3(P)]+ incorporating a rare, bidentate NC‐chelating pyridylpyridylidene ligand are reported. The phosphorus‐based ligand P is either 2,4,6‐triphenylphosphinine or triphenylphosphine. These mononuclear complexes have been fully characterised in solution and by single‐crystal X‐ray diffraction analysis. UV/Vis absorption and photoluminescence spectroscopy studies reveal strong phosphorescence from the phosphinine compound at 77 K but no emission from its triphenylphosphine analogue. This contrasting behaviour can be traced to the π‐acceptor ability of the phosphabenzene ring, as corroborated by electrochemical and time‐dependent DFT (TD‐DFT) calculations. Two cycloplatinated complexes with a rare bidentate pyridylpyridylidene NC ligand and triphenylphosphine or 2,4,6‐triphenylphosphinine coligands are synthesised and characterised. The phosphinine compound is strongly phosphorescent at 77 K, in contrast to the triphenylphosphine counterpart; this behaviour is probably the result of the exceptional π‐acceptor ability of the phosphabenzene ring.